JPS5983625A - Stretch/cling film of olefin polymer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

The present invention relates to olefin polymer films, and more particularly to stretch/cling (i.e., self-adhesive) films for various packaging and/or pallet packaging applications.
The present invention relates to olefin polymer films that have a combination of physical properties that make them particularly well suited for use as films. In another aspect, the present invention relates to biaxially oriented films of ethylene/higher alpha-olefin copolymers loaded with tackifiers. In the art of packaging/pallet wrapping, it is well known to wrap individual articles using the so-called "stretch wrapping" technique and/or to bundle or palletize several articles together. . According to such techniques, a relatively thin film web of polymeric material is stretched or stretched, thereby creating tension sounds in the film web as it is wrapped several times around the article or articles to be packaged or palletized.

[7. Upon release of the stretching or stretching force at the end of the wrapping operation, the film tends to at least partially relax or spring back to its original unstretched dimensions;
This allows it to adhere tightly or snugly to the article or articles encased inside. In connection with such stretch-wrapping operations, the stretched and wrapped film may be held in place around the wrapped part or articles in various ways (i.e., the desired effect on the wrapped article or articles). It is theoretically possible to maintain the stressed dimensions or tension without imparting full integrity to the packaging (retaining the stressed film from returning to its original dimensions or loosening). It is. However, as a matter of practical expediency, efficiency and economy, it is desirable to prevent noticeable slippage of the stretched film layers, thereby reducing the film to its original unstretched dimensions. It is common practice to use films that exhibit sufficient self-adhesive properties (cling properties) to hold the film in place around the packaged article to prevent it from loosening or shrinking back. Although a variety of films are currently available on the market for use in stretch/cling packaging or pallet packaging operations, all such currently available films suffer from one or more notable defects, shortcomings or I am suffering from limitations. For example, some of the films currently available are manufactured using a cast film process. Although such cast films are typically characterized by high Elmendorf tear strength in the transverse direction,
These films generally have relatively low tear resistance in the machine direction. As such, these films have a significant tendency to tear, primarily at the corners or other sharp protrusions of the stretch-wrapped or palletized article. On the other hand, certain other currently available stretch/cling films, such as those produced by conventional blown film processing techniques, have values between Elmendorf tear strengths in the machine direction and the 'R'j direction. Although it has an acceptable balance in general, it has certain other properties, such as its clingability (self-adhesiveness), especially in the case of high elongation, etc., which should be satisfactory to the gold, J: 9 Inferior to general. In view of the aforementioned deficiencies of stretch/cling films available to date, these deficiencies have all been overcome to make them particularly well suited for use as stretch/cling films in packaging and pallet wrapping end-use applications. It would be highly desirable to provide a polymeric film with suitable lamination properties. The present invention has a CAJ (α) machine direction Elmendorf tear strength of at least 2507/mil, and (b) m machine direction:transverse direction Elmendorf tear strength ratio of at least 0.5.
, and (C) the Kling value is at least 102 per sample width of 12.7 cm (C5 inches), and (α
) an ethylene-based copolymer consisting in the polymerized form of a major proportion of ethylene and a minor proportion of higher α-olefin monomers having 6 or more carbon atoms; Stretch/cling films comprised of olefin polymer compositions. The stretch/cling films of the present invention embody an overall combination of properties not previously seen in prior art stretch/cling films. For example, the mechanical direction Elmendorf tear strength of the stretch/cling film of the present invention and the Elmendorf tear strength ratio of MD:TD are particularly noteworthy and advantageous in that are superior to those of conventional stretch/cling films produced on the backing of paper, and therefore are suitable for use in bundle t-stretch wrapping of articles with sharp edges or corners or other sharp protrusions. The stretch/cling films of the present invention also have better surface smoothness and cling properties than previously achieved using internal tackifiers in combination with conventional blown film manufacturing techniques. The olefin polymer resin used to make the stretch/cling films of the present invention contains a major proportion by weight of ethylene and a minor proportion by weight of 6 or more carbon atoms copolymerized therewith. High-grade α-olefin with
It is an ethylene copolymer consisting of Such ethylene-based copolymers are commonly referred to in the art as linear low density polyethylene (LLDPE). Preferably, the ethylene copolymer used has 2 to 10 parts (11%) of the above-mentioned higher α-olefin monomers in a copolymerized state. -hexene, 1
-C6-C□2α-olefins such as heptene, 1-octene, 1-nonene, l-decene, especially 1-hexene, 1
-Heptene or 1-octene is preferred. Although not particularly critical, the above-mentioned ethylene-based copolymers used in the practice of this invention are AST
a melt index of 1 to 10 decigrams/minute (preferably 1 to 5 decigrams/minute), and 0.915 to 0.930 t, as measured according to Condition E of M-D-1238.
/cC (preferably 0.915 to 0.925 f/CC
) typically has a density in the range. As already mentioned, particularly advantageous features of the stretch/cling films of the invention are e.g.
has an Elmendorf tear strength value of at least about 2505
' / mil (preferably at least about 300 f/mil) and by having a ratio of Elmendorf tear strength in the machine direction (CMU):transverse direction (TD) of at least about 0.5 (preferably at least about 0.6). As evidenced by the fact that the film has a relatively high Elmendorf tear strength in the machine direction. Have you conducted any experiments related to the present invention regarding this 9'4r characteristic? The iJf investigation was conducted to determine the Elmendorf tear strength in the machine direction of the stretch/cling film of the present invention and the MD:TD Elmendorf strength ratio -1. It has been shown that the decrease in the amount of water is significantly reduced even when made from blends of the aforementioned ethylene-based copolymers that do not contain in admixture. Therefore, the stretch/cling film of the present invention ff1ff
It is believed that it is an important aspect of the invention that the polymer composition used to prepare the polymer composition consists essentially of the ethylene-based copolymer described above and an effective amount of a suitable tackifier. The tackifier preferably used in the present invention, when blended with the above-mentioned ethylene-based copolymers, increases the tackiness or clinging properties (self-viscosity Mt!fE) f on at least one major surface of the film produced therefrom. It is a substance that can be applied. The term "increased viscosity or clinging" refers to the combination of the ethylene copolymer and tackifier described above.
At least one major surface of a film made from a polymer composition comprising a tackifier has a significantly higher cling property than either major surface of a film made from an otherwise identical polymer composition. It means to have. Representative materials useful as tackifiers herein include hydrocarbon resins such as terpene resins, hydrogenated resins, and resin esters, as well as tactical and atactic polypropylenes, polybutenes, and the like. Particularly useful in the practice of this invention are atactic polypropylene and polybutenes, particularly isobutylene polymers. Preferably used isobutylene polymers have relatively low molecular weights, ie less than 3000 as measured by gel permeation chromatography, more preferably 1
It has a number average molecular weight of 500 to 2,500. In other words, the preferable actectic polypropylene,
5 (>00, more preferably from 2000 to 4o00. Most preferably, the tackifier is a polyimbutylene having a number average molecular weight from 500 to 2500. , the tackifier described above is applied to at least one major surface of the polymeric film in an amount of at least 101 tackifiers per 5 inch sample width as measured according to the Kling test method described in Example 1 below.
(preferably at least 15 per 12.7 Crn sample width)
2) is used in an amount sufficient to give the initial, as-manufactured Kling value. Preferably, the tackifier is a tackifier, even when stretched so that the resulting stretch/cling film has a tensile strength of 150 (most preferably 200) in the machine direction when used in conventional stretch/cling wrapping or bullet wrapping operations. It is used in such an amount that it retains its self-adhesive properties even when stretched to give it a certain amount of elongation. In practice, the adhesive feed needles to be used in the stretch/cling films of the present invention to accomplish one or more of the foregoing objectives may include the specific adhesives selected for use herein. the tackifier, the manner in which the tackifier is dispersed in or throughout the film, the surface properties (i.e., smoothness) of the polymeric film, and the intended end use of the film. Much depends on. That is, for example, in the case of a film intended for stretch/cling wrap applications, including uses at relatively low levels of elongation (such as meat wrap applications), relatively low levels of tackifier C, e.g. A small amount of tackifying agent (approximately 1% by weight, based on the total film weight, and based on a homogeneous blend of single-layer film-type structures), with favorable results when used on a representative basis.
I can do it. On the other hand, in the case of a film intended for use at a relatively high level of elongation (e.g., use in pallet packaging, bundled packaging, etc.), elongation at a relatively high level (e.g., total film weight Based on the single layer film type construction of the blend, the use of at least 300 g of tackifier is typically required. Of course, since cling (self-adhesiveness) is a surface-related phenomenon in films of the type encompassed by this invention, the minimum required amount of tackifier use is limited to tackifying properties within the film structure. Increased concentration of tackifier in at least one or both major surfaces of the film structure by intentional non-uniform distribution of the agent, e.g. using well-known co-extrusion techniques; or the central stone layer may be slightly reduced or minimized (in the sense of minimum weight, using total film weight as a basis) by making it substantially free of adhesion agents. It will be understood by those skilled in the art that this can be done. Thus, for example, in one preferred embodiment of the invention, the stretch/cling film is
The first ethylene/higher α-olefin copolymer layer (
at least one ethylene/higher alpha-olefin copolymer that a) constitutes at least 50 inches (preferably at least 70%) of the total film thickness; and (b) does not incorporate a significant amount of tackifier; It is a multilayer structure in which the surface layer contains an effective amount of tackifier (1.5 to 10% by weight, preferably 3 to 8% by weight, based on the weight of the surface layer). In another preferred embodiment, said multilayer structure comprises a first
The tackifier-free layer is a stone layer placed over medium heat, and these 112 layers are sandwiched between two viscous layers. Thus, for the film construction and end-use related variations, the tackifier will typically be 0.5-1.
It can be said that it is used in groups ranging from 0 weight percent (preferably 1 to 8 weight percent to 11 weight percent). An additional 9" feature of some significance to the stretch/cling film of the present invention (and particularly related to its essential cling properties) is that the film has a relatively smooth surface. For the purposes of the present invention, suitable surface smoothness is defined as a conventional type of Gaydirr.
, er G1. Preferably, this is evidenced by a film having a 60 gloss of at least about 110 as measured using an ossimeter f. Most preferably, the film of the invention is the Gardi-Ber Glossi film described above.
meter '< at least 1 when measured using
It shows a 60° gloss of 20. The thickness of the stretch/cling film of the present invention is not particularly critical. However, in general, its thickness is typically 1d12.7 to 50.8 microns (0.5 to 50.8 microns).
2 mil), preferably in the range of 17.8 to 25.
It is in the range of 4 microns (0.7-1 mil). In the preparation of the stretch/cling films of the present invention, it is believed that it is important to biaxially orient the film in order for the film to have the requisite MD tear strength and MD:TD tear strength ratio as described above. Additionally, the film is quenched fairly quickly after its extrusion, such as a quench rate characteristic of greater than that of conventional cast film methods, as opposed to the generally slower quench rates typically provided by conventional blown film manufacturing techniques. It is also believed that rapid quenching is essential (e.g., due to acceptable surface smoothness in filling with the refining agent and the requisite degree of clinging). Combinations of the aforementioned process features can be achieved in various well-known ways (
For example, conventional cast film extrusion for rapid quenching combined with well-known tentering techniques for biaxial orientation and water quenching for rapid cooling after 7 inches. Although conventional blown film extrusion is suitable for purposes of the present invention, the film extrusion process and apparatus described in U.S. Pat. No. 3,976,733 and U.S. Pat. It has been found to be advantageous and suitable for the purpose of the present invention to produce the entire stretch/cling film as intended. As previously mentioned, the trench/cling films of the present invention are particularly well suited for use in trench/cling wrapping and/or pallet wrapping applications well known in the art. Therefore, the use of such films in such packaging and/or pallet packaging operations is not suitable for stretch/
Methodologies and techniques well known to those skilled in the art of cling packaging and pallet packaging are generally followed. Similarly, the stretch/cling films of the present invention may also contain additives commonly used in conventional stretch/cling film compositions, such as pigments, dyes, opacifying agents, antioxidants, UV stabilizers, and the like. The present invention will be explained in more detail with the following examples.
The invention should not be construed as being limited by these examples. In these examples, all parts and parts are by weight unless otherwise specified. Example 1 U.S. Patent Nos. 3,976,733 and 4,025
, 253, with a blowing ratio of 2.5:1 and a quench temperature of 30°C (below 86°C), a two-layer film with a thickness of 20 microns (0.8 mil) on the gold side was prepared. Manufactured. The first layer of the film has a total film thickness of 7
0%, melt index of 2.3 dg/min and 0.917? The polymer was composed of an ethylene/octene copolymer (a linear low density polyethylene (CLLI), PE) with a density of /cI-gold, commercially available from The Dow Chemical Company under the trade name OWLEX 2047. The remaining layers of the film (constituting 30 φ of total film fill) are 95% by weight based on the blended heavy phase of DOWLEX 2047 (LLI) PE and 5% by weight based on the total blend weight. The properties of the resulting film product are summarized in Table 1 below. The corresponding properties of a commercially available stretch/cling film sold under the trade name MOBILRAP'E'X by Mobil Chemical Corporation for this purpose are also shown. Table 1 Film Properties Example 1 Film Commercially available comparative film 1, Elmendorf tear strength (2/mij.) machine direction
478 78 Lateral direction 625 7442.60° Glossiness 140 1253° Cring Note (f/12.7Crn) (f15-4-)
'24 54, Shrinkage (negative values indicate shrinkage, positive values indicate elongation) Machine direction -63°2
-85.4 Lateral direction +9.2 +
51.35, tensile strength at yield point Si K
v/lri psi Kg/di machine direction
1311 92 2245 15
7 Lateral direction 1046 73 1039 73
6. Final tensile strength -Ky/cr
d ps i Kg/ca machine direction
4319 302 6297 441 Lateral 3694 258 3900 273
7. Final elongation (chi) machine direction 650
500 wood This is not an embodiment of the present invention. The reported clingability values are based on a cylindrical metal roller having a weight of 1 bond, a length of at least 12.7/-rn (5 inches), and a diameter of 0.48 mm (6 inches). across the entire width of the film sample (i.e. the entire weight of the roller is supported across the entire width of the film sample as it passes through the roller and is evenly distributed over the entire 11V). (in a manner) and the weight t7 applied to the equation υ over at least that portion of the length of the film sample to be measured.
] Under pressure and pressure, the outer surface of the extruded tube and the inner surface of the extruded tube were newly bonded together. 12.
7α width x 22.9Crn length 5 inches lJ'ij
is the average force required to completely peel or separate two film samples of length x 9 inches, expressed in y numbers. When measuring the ring value in this way, the peeling of the two film samples Prl#(rJ,' 23 tyn/
(9 inches/minute) and a constant peel angle of 60°. The peel angle is measured between the top surface of the part of the top film sample layer that has already been peeled off and the top surface of the top film sample layer that is about to be peeled off due to instantaneous contact. Each of the above films was used for stretch wrapping evaluations on commercial scale stretch wrapping equipment with a pre-stretch system. The test specimen used for such evaluation had a height of 1.83 m (72 in), a width of 1.22 m (48 in) and a width of 1.2277 m (72 in).
L (48 inches) deep plywood box, which was placed on a typical wooden knotlet. This evaluation measures the minimum film weight required to wrap the box, the stretch at which the film's cling properties become inadequate, and the film no longer maintains its integrity around sharp corners and edges at the top of the box. It consisted of measuring elongation when full retention could not be achieved. The results of these tests are listed in Table 1 below. Table ■ Film t'JE 2K Film of Example 1 Commercially available comparative film □ 1. Minimum weight (oz) (4,0)
(5,8) grams 113 14
22. Kling elongation limit (circulation) 240
As is clear from the results shown in Tables 1 and 2 on the 109 wrapped pallet, the film of Example 1 has a higher GzMJJ two-directional Ndolf tear strength, (
b) g, mechanical:transverse Elmendorf tear strength ratio;
(C) initial cling, strength values, and (d) maximum elongation limit based on both loss of cling and corner failure criteria. Comparative Experiment Example 1's bivalent ethylene/octene copolymer components were combined in both film layers with 95 wt.% of the same ethylene/octene copolymer and 5 wt.% of conventional low-density polyethylene homopolymer (density 0.922 f/cc, A film sample similar to Example 1 was prepared according to the method of Example 1, except that a blend consisting of a melt index of 1.15 decigrams/min) and a force of 1.15 decigrams per minute) was substituted. The resulting film sample had a machine direction Elmendorf tear strength of 1172/mil and a machine direction:transverse direction Elmendorf tear strength ratio of 0.176. Thus, this comparative experiment demonstrates the importance of ensuring that the ethylene-based polymer component used in the present invention consists essentially of ethylene/higher alpha-olefin polymers as described above. Although the invention has been described and illustrated with reference to specific aspects and embodiments thereof, such fact should not be construed as limiting the scope of the invention. Patent applicant The Dow Chemical Company Representative Patent attorney Ryoji Kawase

Claims (1)

[Claims] 1, 64) (a) an Elmendorf tear strength in the machine direction of at least 2501/mil; (b) a ratio of Elmendorf tear strength in the machine direction:transverse direction of at least 0°5.
, and (c) the Kring value is at least 102 per 5 inch sample width, and (α) the polymerized form contains a major proportion of ethylene and a minor proportion of 6 or more carbon atoms. (b)
A stretch/cling film comprised of an olefin polymer composition consisting essentially of a 7F# effective amount of a viscosity additive. 2. A stretch/cling film according to claim 1 which retains self-adhesive properties even when stretched to 150% elongation in the machine direction. 3. The stretch/cling film of claim 1 which retains its full self-adhesive properties even when stretched to a stretch of 200 inches in the machine direction. 4. The stretch/cling film of claim 1, having a machine direction:transverse direction Elmendorf tear strength ratio of at least 0.6. 5. The stretch/cling film according to claim 1, wherein the tackifier 24 is used in an amount of 0.5 to 1% by weight based on the total weight of the reflex polymer composition. 6. The stretch/cling film of claim 5, wherein the tackifier is used in an amount equal to or less than 1.5 weights based on the total weight of the all-olefin polymer composition. 7. The stretch/cling film according to claim 1, wherein the tackifier is polyisobutylene. 2. The stretch/cling film according to claim 1, wherein the higher α-olefin monomer of the B, x-thin copolymer is a C6 to C1□ α-olefin. 9. The stretch/cling film according to claim 1, wherein the higher α-olefin monomer component constitutes 2 to 10 weight percent of the ethylene copolymer. 10. (/1) a first polymer layer comprising at least about 50% of the total thickness of the stretch/cling film and not incorporating a significant amount of tackifier;
2. A stretch/cling film according to claim 1, comprising at least one surface layer incorporating an effective amount of a tackifier. 11. The stretch/cling film according to claim 10, wherein the tackifier constitutes 1.5 to 10% by weight of the surface layer. 12. Claim No. 1, comprising two surface layers containing an effective amount of a tackifier, the first polymer layer comprising six layers sandwiched between these two surface layers. Stretch/cling film according to item 10. 13. The stretch/cling film according to claim 40, wherein the tackifier constitutes 3 to 8 weight 1i of the surface layer.